In the helicopter field, there have been retractable helicopter rotors, however, these prior art constructions added substantial weight to the helicopter and required substantial disassembly of parts to move the helicopter rotor from its extended position to its retracted position, and substantial assembly work to move the helicopter from its retracted position to its extended position. The prior art also required some external means for raising and lowering the rotor, such as a crane. U.S. Pat. No. 3,972,491 granted on Aug. 3, 1976 to Donald L. Ferris et al. discloses a two-position main rotor wherein the rotor is supported for rotation about an axis by an extension shaft which is, in turn, supported from the main rotor drive shaft which is, in turn, supported from the helicopter fuselage.
In the flight mode of operation, the extension shaft is connected at one end to the main rotor hub via a first series of fasteners and connected at the other end to the main rotor shaft by a second series of fasteners. As such, the configuration taught by Ferris et al. requires the disengagement of both upper and lower fasteners to move the rotor from its extended to its retracted position and reengagement of those fasteners to move the rotor from its retracted to its extended position. Further, these fasteners and their associated hardware impose weight penalties upon the helicopter. The Ferris et al. construction also requires connection and disconnection of the helicopter pitch change rods.
To put the Ferris et al. construction back into flight mode, it is not only necessary to reassemble all of the parts disassembled during the operation of retracting the rotor, but also reconnecting the pitch change rods and flying dedicated flights to re-establish rotor track and balance.